Hydrosilylation chemistry, typically involving a reaction between a silyl hydride and an unsaturated organic group, is the basis for synthetic routes to produce commercial silicone-based products like silicone surfactants, silicone fluids and silanes as well as many addition cured products like sealants, adhesives, and silicone-based coating products. See, for example, US Patent Application Publication 2011/0009573A1 to Delis et al. Typical hydrosilylation reactions use precious metal catalysts to catalyze the addition of a silyl-hydride (Si—H) to an unsaturated group, such as an olefin. In these reactions, the resulting product is a silyl-substituted, saturated compound. In most of these cases, the addition of the silyl group proceeds in an anti-Markovnikov manner, i.e., to the less substituted carbon atom of the unsaturated group. Most precious metal catalyzed hydrosilylations only work well with terminally unsaturated olefins, as internal unsaturations are generally non-reactive or only poorly reactive. There are currently only limited methods for the general hydrosilylation of olefins where after the addition of the Si—H group there still remains an unsaturation in the original substrate. This reaction, termed a dehydrogenative silylation, has potential uses in the synthesis of new silicone materials, such as silanes, silicone fluids, crosslinked silicone elastomers, and silylated or silicone-crosslinked organic polymers such as polyolefins, unsaturated polyesters, and the like.
Various precious metal complex catalysts are known in the art. For example, U.S. Pat. No. 3,775,452 discloses a platinum complex containing unsaturated siloxanes as ligands. This type of catalyst is known as Karstedt's catalyst. Other exemplary platinum-based hydrosilylation catalysts that have been described in the literature include Ashby's catalyst as disclosed in U.S. Pat. No. 3,159,601, Lamoreaux's catalyst as disclosed in U.S. Pat. No. 3,220,972, and Speier's catalyst as disclosed in Speier, J. L, Webster J. A. and Barnes G. H., J. Am. Chem. Soc. 79, 974 (1957).
There are examples of the use of Fe(CO)5 to promote limited hydrosilylations and dehydrogenative silylations. (See Nesmeyanov, A. N.; Freidlina, R. Kh.; Chukovskaya, E. C.; Petrova, R. G.; Belyaysky, A. B. Tetrahedron 1962, 17, 61 and Marciniec, B.; Majchrzak, M. Inorg. Chem. Commun. 2000, 3, 371). The use of Fe3(CO)12 was also found to exhibit dehydrogenative silylation in the reaction of Et3SiH and styrene. (Kakiuchi, F.; Tanaka, Y.; Chatani, N.; Murai, S. J. Organomet. Chem. 1993, 456, 45). Also, several cyclopentadiene iron complexes have been used to varying degrees of success, with the work of Nakazawa, et at showing interesting intramolecular dehydrogenative silylation/hydrogenation when used with 1,3-di-vinyldisiloxanes. (Roman N Naumov, Masumi Itazaki, Masahiro Kamitani, and Hiroshi Nakazawa, Journal of the American Chemical Society, 2012, Volume 134, Issue 2, Pages 804-807).
A rhodium complex was found to give low to moderate yields of allyl-silanes and vinyl silanes. (Doyle, M. P.; Devora G. A.; Nevadov, A. O.; High, K. G. Organometallics, 1992, 11, 540-555). An iridium complex was also found to give vinyl silanes in good yields. (Falck, J. R.; Lu, B, J. Org Chem, 2010, 75, 1701-1705.) Allyl silanes could be prepared in high yields using a rhodium complex (Mitsudo, T.; Watanabe, Y.; Hori, Y. Bull. Chem. Soc. Jpn. 1988, 61, 3011-3013). Vinyl silanes could be prepared through the use of a rhodium catalyst (Murai, S.; Kakiuchi, F.; Nogami, K.; Chatani, N.; Seki, Y. Organometallics, 1993, 12, 4748-4750). Dehydrogenative silylation was found to occur when iridium complexes were used (Oro, L. A.; Fernandez, M. J.; Esteruelas, M. A.; Jiminez, M. S. J. Mol. Catalysis, 1986, 37, 151-156 and Oro, L. A.; Fernandez, M. J.; Esteruelas, M. A.; Jiminez, M. S. Organometallics, 1986, 5, 1519-1520). Vinyl silanes could also be produced using ruthenium complexes (Murai, S.; Seki, Y.; Takeshita, K.; Kawamoto, K.; Sonoda, N. J. Org. Chem. 1986, 51, 3890-3895.).
A palladium-catalyzed silyl-Heck reaction was recently reported to result in the formation of allyl-silanes and vinyl silanes (McAtee J R, et al., Angewandte Chemie, International Edition in English (2013, 51, 3663-3667 (Apr. 10, 2012)).
U.S. Pat. No. 5,955,555 discloses the synthesis of certain iron or cobalt pyridine di-imine (PDI) dianion complexes. The preferred anions are chloride, bromide and tetrafluoroborate. U.S. Pat. No. 7,442,819 discloses iron and cobalt complexes of certain tricyclic ligands containing a “pyridine” ring substituted with two imino groups. U.S. Pat. Nos. 6,461,994, 6,657,026 and 7,148,304 disclose several catalyst systems containing certain transitional metal-PDI complexes. U.S. Pat. No. 7,053,020 discloses a catalyst system containing, inter alia, one or more bisarylimino pyridine iron or cobalt catalyst. Chirik et al describe bisarylimino pyridine cobalt anion complexes (Inorg. Chem. 2010, 49, 6110 and JACS. 2010, 132, 1676.) However, the catalysts and catalyst systems disclosed in these references are described for use in the context of olefin hydrogenation, polymerizations and/or oligomerisations, not in the context of dehydrogenative silylation reactions.
There is a continuing need in the silylation industry for non-precious metal-based catalysts that are effective for efficiently and selectively catalyzing dehydrogenative silylations. The present invention provides one answer to that need.
Further, many industrially important homogeneous metal catalysts suffer from the drawback that following consumption of the first charge of substrates, the catalytically active metal is lost to aggregation and agglomeration whereby its beneficial catalytic properties are substantially diminished via colloid formation or precipitation. This is a costly loss, especially for noble metals such as Pt. Heterogeneous catalysts are used to alleviate this problem but have limited use for polymers and also have lower activity than homogeneous counterparts. For example, it is well-known in the art and in the hydrosilylation industry that the two primary homogeneous catalysts, Speier's and Karstedt's, often lose activity after catalyzing a charge of olefin and silyl- or siloxyhydride reaction. If a single charge of the homogeneous catalyst could be re-used for multiple charges of substrates, then catalyst and process cost advantages would be significant.